You can get this error in Plan Management module when you have clicked into the Invoice and you are trying to send it off for approval.
Screenshot of error:
The error is saying that there needs to be a single active "Invoice / Quote" type document and in the below example there are zero eligible documents.
The only "Invoice / Quote" type document is Hidden (i.e. not active) because the status button says you can "Restore" it and the amended invoice is not of type "Invoice / Quote" type document because that was added as manual text instead of selecting from the dropdown when uploading the file.
You can successfully get the approval email sent by simply adding the invoice document for it to attach as the correct type.
BEFORE:
AFTER:
Note that all you need to do is download the Amended invoice (#2 in the list from AFTER) and uploaded that document again as type "Invoice / Quote" and just ensure that there is only one active document of type "Invoice / Quote".
The reason is that Careflo is looking for a single Invoice document to attach in the Approval email.